In recent years, the petroleum industry has invested heavily in the development of improved marine survey techniques and seismic data processing methods in order to increase the resolution and accuracy of seismic images of subterranean formations. Marine surveys illuminate a subterranean formation located beneath a body of water with acoustic signals produced by one or more submerged seismic sources. The acoustic signals travel down through the water and into the subterranean formation. At interfaces between different types of rock or sediment of the subterranean formation a portion of the acoustic signal energy may be refracted, a portion may be transmitted, and a portion may be reflected back toward the formation surface and into the body of water. A typical marine survey is carried out with a survey vessel that passes over the illuminated subterranean formation while towing elongated cable-like structures called streamers. The streamers may be equipped with a number of collated, dual pressure and particle motion sensors that detect pressure and vertical particle motion wavefields, respectively, associated with the acoustic signals reflected back into the water from the subterranean formation. The pressure sensors generate seismic data that represents the pressure wavefield and the particle motion sensors generate seismic data that represents the vertical particle motion wavefield. The survey vessel receives and records the seismic data generated by the sensors.
A wavefield that travels upward from the subterranean formation and is detected by the pressure or particle motion sensors is called an up-going wavefield, which alone may be used to compute a seismic image of the subterranean formation. However, the surface of the water acts as a nearly perfect acoustic reflector. As a result, the sensors also detect a down-going wavefield created by reflection of the up-going wavefield from the water surface. The down-going wavefield is essentially the up-going wavefield with a time delay that corresponds to the amount of time it takes for acoustic signals to travel up past the streamers to the water surface and back down to the streamers. The down-going wavefield combines with the up-going wavefield, resulting in recorded seismic data contaminated with, unwanted down-going wavefield energy that creates “ghost” effects in seismic images of the subterranean formation computed from the seismic data. Typical seismic data processing techniques use both the pressure wavefield and vertical particle motion wavefield to separate the pressure and vertical particle motion wavefields into up-going and down-going wavefields. The up-going wavefield may be used to compute an image of a subterranean formation without the ghost effects caused by the down-going wavefield.